Teenage suicide is the provocative topic that Picoult plumbs, with mixed results, in her fifth novel. Popular high-school swimming star Chris Harte and talented artist Em Gold bonded as infants; their parents have been next-door neighbors and best friends for 18 years. When they fall in love, everyone is ecstatic. Everyone, it turns out, except for Em, who finds that sex with Chris feels almost incestuous. Her emotional turmoil, compounded by pregnancy, which she keeps secret, leads to depression, despair and a desire for suicide, and she insists that Chris prove his love by pulling the trigger. The gun is fired in the first paragraph, and so the book opens with a jolt of adrenaline. But Picoult stumbles in delineating both sets of parents' responses to the tragedy. Unconvincing behavior and dialogue inappropriate to the situation (plus, most importantly, the fact that the parents fail to discuss crucial topics) never touch the essence of bereavement and thus destroy credibility. Picoult redeems herself in flashbacks that reveal the two marital relationships and the personalities of both couples; and she sensitively explores the question of how well parents can ever know their children. After Chris is accused of murder and jailed, the narrative acquires impressive authenticity and suspense, with even the minor characters evoked with Picoult's keen eye for telling detail. The courtroom scenes (reminiscent of Picoult's 1996 novel, Mercy), are taut and well paced. Readers may remain unconvinced, however, that an intelligent young man like Chris would not have sought some help rather than respond to his lover's desperate request. Literary Guild and Doubleday Book Club selections; foreign rights sold in Germany, France, Poland and Norway. (May)